1. Field of the Invention
The present invention relates to a fluid filled vibration damping device adapted to provide active vibration damping action through control of pressure fluctuations of a pressure receiving chamber that is filled with a non-compressible fluid, the control being carried out in a cycle that corresponds to the frequency of the vibration to be damped.
2. Description of the Related Art
In the field of vibration damping devices such as vibration damping linkages or vibration damping supports designed for installation between components that make up a vibration transmission system, one type of known device is a fluid filled type vibration damping device having a first mounting member and a second mounting member linked by a rubber elastic body; a pressure-receiving chamber whose wall is partially defined by the rubber elastic body and an equilibrium chamber whose wall is partially defined by a flexible film, the pressure-receiving chamber and the equilibrium chamber being formed to either side of a partition member and filled with a non-compressible fluid; and an orifice passage connecting the pressure-receiving chamber and the equilibrium chamber. Since this type of fluid filled vibration damping device is able to exhibit vibration damping effect by using flow action, e.g. resonance action, of fluid flowing through the orifice passage, application of such devices in automotive engine mounts and the like is a current topic of interest.
Active type fluid filled vibration damping devices are one type of fluid filled vibration damping device as discussed above. In such an active vibration damping device, typically, another part of the wall of the pressure-receiving chamber will be constituted by an oscillating plate, and an electromagnetic actuator will be disposed to the opposite side of the pressure-receiving chamber, with the oscillating plate between them. A coil member making up part of the electromagnetic actuator is fixedly supported on the second mounting member, and an output member that is subjected to driving force when electrical current is supplied to the coil member is affixed to the oscillating plate. With this arrangement, oscillation by the oscillating plate is actuated through control of current to the coil member with reference to the vibration to be damped, in order to control the vibration damping performance through control of pressure in the pressure-receiving chamber.
The oscillating plate employed in an active vibration damping device of this kind will in some instances be formed from a rubber elastic body for example. However, in order to ensure an effective piston surface area, it is preferable for the plate to be composed of a rigid member of metal, synthetic resin, or the like, as taught in U.S. Pat. No. 6,422,546.
However, in the fluid filled vibration damping device disclosed in U.S. Pat. No. 6,422,546, with the aim of providing the oscillating plate with elastically positioned support while ensuring fluid-tightness on the part of the pressure-receiving chamber, the oscillating plate is linked to the second mounting member via a supporting rubber elastic body of annular shape. For this reason, there is a anxiety that, owing to permanent set in fatigue of the supporting rubber elastic body, it will be difficult to consistently achieve the desired vibration damping action. Another problem is that oscillation energy of the oscillating plate will be consumed through deformation of the supporting rubber elastic body, and thus power consumption will be high.
Accordingly, in Japanese unexamined Patent Publication No. JP-A-2005-291276, the Applicant proposed a fluid filled vibration damping device incorporating an oscillating plate of piston design. In this fluid filled vibration damping device, a portion of the wall of the pressure-receiving chamber is defined by a cylinder member of hollow round tubular shape, and the output member of the electromagnetic actuator is provided at the distal end thereof in the actuation direction with an oscillating plate of piston shape. A gap is provided between the outside peripheral face of the oscillating plate and the inside peripheral face of the cylinder member, while the oscillating plate is displaceable in the axial direction along the inside peripheral face of the cylinder member. Through appropriate design of the planar dimensions and of the gap between the inside peripheral face of the cylinder member and the outside peripheral face of the oscillating plate, it is possible to control pressure of the pressure-receiving chamber in association with oscillation of the oscillating plate, while ensuring that pressure fluctuations of the pressure-receiving chamber are such that the orifice effect is maintained.
The gap between the inside peripheral face of the cylinder member and the outside peripheral face of the oscillating plate will be sufficiently small so as to inhibit pressure leakage from the pressure-receiving chamber through the gap. Additionally, in order to ensure large planar dimensions of the opposed faces of the oscillating plate and the cylinder member with a view to inhibiting pressure leakage from the pressure-receiving chamber, it will be preferable for the inside peripheral section of the cylinder member and of the outside peripheral section of the oscillating plate to have considerable axial length.
However, where the gap between the cylinder member and the oscillating plate is small and their opposed faces extend for considerable length in the axial direction, there is an anxiety that the oscillating plate will interfere with the inside peripheral face of the cylinder member.
In particular, owing to factors such as the pressure distribution of the pressure-receiving chamber and twisting displacement of the actuator output shaft, the oscillating plate will tend to interfere with the cylinder inside face through twisting displacement in the axial direction. When the oscillating plate experiences displacement in the axial direction while interfering with the cylinder member in this way, not only will the actuation efficiency of the oscillating plate be reduced, but there will also be an anxiety of damage to the opposing faces of the oscillating plate and/or the cylinder member. Furthermore, if seizing should occur, there is an anxiety that electromagnetic actuator may operate improperly of become non-operational, or that noise and vibration may result.